(1) Still running on 5.6.7, I just now triggered the "semi-freeze" while using Adobe Acrobat to edit a pdf file, so it looks like the problem is not the kernel. It must be the qemu-system-X86 upgrade.
(2) from ps aux:
libvirt+ 1054382 79.4 32.4 13622764 10627784 ? Rl 12:17 11:41 /usr/bin/qemu-system-x86_64 -name guest=win10,debug-threads=on -S -object secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-2-win10/master-key.aes -machine pc-i440fx-2.12,accel=kvm,usb=off,vmport=off,dump-guest-core=off -cpu Skylake-Client-IBRS,hv-time,hv-relaxed,hv-vapic,hv-spinlocks=0x1fff -m 10240 -overcommit mem-lock=off -smp 4,sockets=4,cores=1,threads=1 -uuid e98b6bf6-d366-44c3-a529-790924d99373 -no-user-config -nodefaults -chardev socket,id=charmonitor,fd=33,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=localtime,driftfix=slew -global kvm-pit.lost_tick_policy=delay -no-hpet -no-shutdown -global PIIX4_PM.disable_s3=1 -global PIIX4_PM.disable_s4=1 -boot strict=on -device ich9-usb-ehci1,id=usb,bus=pci.0,addr=0x5.0x7 -device ich9-usb-uhci1,masterbus=usb.0,firstport=0,bus=pci.0,multifunction=on,addr=0x5 -device ich9-usb-uhci2,masterbus=usb.0,firstport=2,bus=pci.0,addr=0x5.0x1 -device ich9-usb-uhci3,masterbus=usb.0,firstport=4,bus=pci.0,addr=0x5.0x2 -device virtio-scsi-pci,id=scsi0,bus=pci.0,addr=0x6 -device virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x7 -blockdev {"driver":"file","filename":"/home/don/Win10/win10.img","node-name":"libvirt-2-storage","auto-read-only":true,"discard":"unmap"} -blockdev {"node-name":"libvirt-2-format","read-only":false,"driver":"qcow2","file":"libvirt-2-storage","backing":null} -device scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=0,device_id=drive-scsi0-0-0-0,drive=libvirt-2-format,id=scsi0-0-0-0,bootindex=1 -blockdev {"driver":"file","filename":"/home/don/Win10/virtio-win-0.1.149.iso","node-name":"libvirt-1-storage","auto-read-only":true,"discard":"unmap"} -blockdev {"node-name":"libvirt-1-format","read-only":true,"driver":"raw","file":"libvirt-1-storage"} -device scsi-cd,bus=scsi0.0,channel=0,scsi-id=0,lun=2,device_id=drive-scsi0-0-0-2,drive=libvirt-1-format,id=scsi0-0-0-2 -netdev tap,fd=35,id=hostnet0 -device rtl8139,netdev=hostnet0,id=net0,mac=52:54:00:e0:b0:51,bus=pci.0,addr=0x3 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -chardev spicevmc,id=charchannel0,name=vdagent -device virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=com.redhat.spice.0 -device usb-tablet,id=input0,bus=usb.0,port=1 -spice port=5900,addr=127.0.0.1,disable-ticketing,image-compression=off,seamless-migration=on -device qxl-vga,id=video0,ram_size=67108864,vram_size=67108864,vram64_size_mb=0,vgamem_mb=16,max_outputs=1,bus=pci.0,addr=0x2 -device intel-hda,id=sound0,bus=pci.0,addr=0x4 -device hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0 -chardev spicevmc,id=charredir0,name=usbredir -device usb-redir,chardev=charredir0,id=redir0,bus=usb.0,port=2 -chardev spicevmc,id=charredir1,name=usbredir -device usb-redir,chardev=charredir1,id=redir1,bus=usb.0,port=3 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x8 -sandbox on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny -msg timestamp=on
EDIT: I just checked with apt, and now we have these updates for qemu:
qemu qemu-kvm qemu-system-common qemu-system-data qemu-system-gui qemu-system-x86 qemu-utils
I have another system that I use for experiments -- I'm going to update that one and see if it is stable.
EDIT #2 -- Installed qemu-system-x86 package is ver. 5.0-2. New version is 5.0-3.